The present invention relates to a novel and improved optoelectrical filling or weft bobbin feeler on a shuttle weaving loom, comprising a casing provided with at least one flat wall mounted in parallel relationship to the shuttle race or slay beam, and a light source and light sensor located in the casing and having optical axes intersecting in a point outside the casing.
Optoelectrical bobbin feelers of that type, briefly termed bobbin feelers in the following context, are disclosed in U.S. Pat. Nos. 3,693,671 and 3,892,492. These known bobbin feelers are provided with a further optoelectrical transducer (light source or sensor) arranged in the spatial angle between light source and light sensor.
The bobbin feeler of the first-named letters patent comprises a light source, a first photocell responding to specularly as well as diffusely reflected light emanating from the source, and a second photocell receiving only light diffusely reflected by the bobbin. The light beam necessary for scanning the bobbin is generated by a D.C.-supplied glow lamp. Discrimination of the conditions "bobbin covered" and "bobbin empty" is based on the fact that the bobbin substantially reflects diffusely when covered with a thread winding, the portion of the specularly reflected light then being small, whereas with the empty bobbin the reflection at the surface thereof is mainly specular.
According to the second-named letters patent, there are provided two alternately pulsed light sources, such as light emitting diodes, and a single light sensor, e.g. a phototransistor.
Usually, the known bobbin feelers are fixedly mounted at the frame of the loom and above one of the shuttle boxes, in such a manner that the optical axes of the optoelectrical transducers form a scanning plane parallel to the slay beam and perpendicular to the horizontal plane. The weft bobbin is scanned in its end position in the shuttle box when the slay is moving towards its frontal end position, i.e. shortly prior to the slay beat-up. During this forward movement of the slay, firstly the front edge and the swell of the shuttle box, followed by the front edge of the shuttle pass through the scanning plane, and finally by the weft bobbin to be scanned. Since said edges normally are smooth and thus are good reflectors, wrong signals may be triggered, simulating the condition "bobbin empty" and thus causing undesired loom stops.